Understanding the Microbial Utilization of Glycerol under Fermentative Conditions

The rising concerns related to the cost, sustained availability, and environmental impact of use of fossil fuels has led to the search for new technologies that generate fuels and materials from renewable carbon sources. Although biofuels such as biodiesel and bioethanol represent a secure, renewable, and environmentally safe alternative to fossil fuels, their economic viability is a major concern. A solution to this problem is the conversion of glycerol, a by-product generated in large amounts in the production of these biofuels, into fuels and chemicals.

The current methods for converting glycerol into more valuable products can be grouped into two main platforms: chemical and biological. The chemical platform takes advantage of traditional chemical catalytic methods while the biological platform utilizes the biocatalytic activities of microorganisms to convert glycerol into desired products. While these chemical conversion techniques are able to produce valuable products, several significant disadvantages exist that make these processes industrially undesirable. Low product specificity, high operating temperatures and pressures, and the inability to use crude glycerol with high levels of contaminants are just some of the disadvantages associated with current chemical conversion techniques. Biological techniques avoid many of these disadvantages directly and provide a means of synthesizing a wide array of products and functionalities. Given highly reduced nature of carbon atoms in glycerol and the cost advantage of anaerobic processes, fermentative metabolism of glycerol is of special interest. In order to utilize these advantages, however, microorganisms able to perform glycerol fermentation in the absence of electron acceptors are required.

Glycerol utilization under fermentative conditions requires cellular processes enabling functions such as the formation of glycolytic intermediates from glycerol, maintenance of an overall redox balance, and the synthesis of ATP via substrate level phosphorylation in the absence of external electron acceptors. The ability of certain microorganisms to utilize glycerol in the absence of external electron acceptors can be grouped into specific models that encompass the genes, enzymes, and metabolic pathways required for these cellular processes enabling fermentative glycerol utilization. The identification and understanding of these specific models for the microbial fermentation of glycerol will provide the fundamental knowledge required as a platform for the metabolic engineering of microorganisms for the use of glycerol as a feedstock for the production of reduced fuels and chemicals.

Our current work is focused on the elucidation of required pathways and mechanisms for several proposed models enabling fermentative glycerol utilization through comprehensive experimental investigation. The investigation takes advantage of the expertise we have developed in the use of both conventional experimental approaches as well as functional genomics and systems biology tools.